The present disclosure relates to a semiconductor laser apparatus.
For example, as a wavelength-tunable light source for Dense Wavelength Division. Multiplexing (DWDM) optical communications, an integrated wavelength-tunable laser element has been disclosed (see, for example, Japanese Laid-open Patent Publication No. 2005-317695 and Japanese Laid-open Patent Publication No. 2008-103766). Japanese Laid-open Patent Publication No. 2005-317695 discloses a wavelength-tunable laser element in which a semiconductor laser array including a plurality of Distributed Feedback (DFB) semiconductor laser elements having different laser emission wavelengths, a Multi Mode Interferometer (MMI) optical coupler, and a Semiconductor Optical Amplifier (SOA) are integrated on a substrate.
When the optical coupler connected to the semiconductor laser array described above does not have wavelength selectivity, the output optical intensity of the light output from the wavelength-tunable laser element is lower than or equal to the output optical intensity of the light output from the semiconductor laser array divided by the number of the semiconductor elements. This increases a loss of the light output from the wavelength-tunable laser element.
In light of the foregoing, to reduce the loss and increase the output efficiency of the element, a wavelength-tunable laser element using an Arrayed Waveguide Grating (AWG) including a semiconductor as an optical coupler is disclosed (see, for example, Japanese Laid-open Patent Publication No. 2008-282937). The AWG includes an inputting slab waveguide, an array waveguide, and an outputting slab waveguide, and an output waveguide is connected to the outputting slab waveguide.
However, when there is a manufacturing error in the AWG, the output position of the AWG changes. due to the change the coupling loss between the AWG and the output waveguide may be increased, and thus the output of the element may be significantly reduced. In other words, in the wavelength-tunable laser element including an output waveguide connected to the outputting slab waveguide, the tolerance to the manufacturing error is small. Especially, the refractive index of the semiconductor material used in the semiconductor laser element is significantly greater than that of a fused quartz-based material. Thus, the tolerance to the manufacturing error of the semiconductor material-based AWG is drastically lower than that of a fused quartz-based AWG. This is a great disadvantage.